A 23-year-old man presents to the clinic for evaluation of new symptoms of low back pain, stiffness, and left eye discomfort. Sunlight also bothers his eyes. The back pain is worse at night and described as a dull ache in the back and buttock area. On physical examination, there is paravertebral muscle, iliac crest, and ischial tuberosity tenderness on palpation. Active range of motion reveals limited forward flexion of the lumbar spine. His eye is also inflamed and the pupil is constricted. Lumbar and pelvic x-rays show sacroiliitis. Which of the following is the most likely diagnosis for his eye symptoms (it is the most common extra-articular manifestation of this condition)?